Electrical reproduction of sound from records



ELECTRICAL REPRODUCTION OF SOUND FROM RECORDS Filed Feb. l2, 1930 2Sheets-S1186?I l Sept. 15, 1931. H. PEARsoN ET AL ELECTRICALREPRODUCTION OF SOUND FROM RECORDS 2 Sheets-Sheet 2 Filed Feb. l2. 1930Patented Sept. 15, 1931 UNITED STATES :Parar Fries iIITJLIIC'JRICALVREPRODUCTION Ol" SOUND FBQLVI` RECORDS M' i Application led February 12,1830. Serial No. 427,764.

This invention comprises improvements in or relating to electricalreproduction of sound from records and has reference to apparatus foruse in the electrical transmission 5 of music, speech and other soundsfrom graniophone records.

In connection with apparatus of this class an electrical device known asa pick up or collector is employed, adapted for attachi0 ment to thetone arm of a gramophone and embodying a metal reed resiliently orpivotally mounted or suspended so as to be capable of a limitedoscillatory movement between the poles of an electromagnet. Detachablycarried by the reed is aneedle adapted to coact with the gramophonerecords in the known manner so that the vibration set up in said needleand reed by the irregularities in the record surface induce in 'Q0 thepole coils of the magnet varying electric impulses which are suitablyamplified and conveyed to a loud speaker such as is used with wirelessreceiving instruments, or other reproducing instrument.

'g5 In order faithfully to reproduce the music, speech or the like inthe loud speaker and prevent distortion it is essential that the reedand needle be normally held from uncontrolled movement `while permittingthe '30 oscillatory motion effected by the record, and to this end it isthe custom to damp the lateral motion of said reed and needle betweenadjustable resilient damping-elements i or cushions.

35 The present invention has reference to the type of pick up comprisinga permanent magnet of the horseshoe type having coil carrying pole tipsassociated with each limb and having a metal reed resiliently mounted oat its upper part and positioned between said pole tips and adapted tobe oscillated to a limited extent bythe needle traversing the grooves ofthe gramophone record tok induce electric currents in the coils of themag- '45 net, aspreviously described.

According to the present invention a pick -up or collector is providedembodying inl -combination a permanent horseshoe mag net, a coil on eachpole piece or tip of said to magnet, a resiliently mounted metal reedbetween said' pole coils, the length of said caf reed approximating thediameter of the pole coils, adjustable reed damping means eX- tendingthrough the pole tips and means for adjustably locking said dampingmeans inet? position relatively to the reed.

A further feature consists in mounting the pick-up upon a hinged orpivoted tone arm which is provided with counter balancing means, thebalance of the tone arm being 1ST 5 advantageously adjustable.

For the purpose of more fully describing the nature of this inventionreference will now be made to the accompanying drawings, wherein zt (i3Figure l shows in part sectional elevation a pick-up or collector inaccordance with this invention.

Figure 2 is a rear view of the device shown in Figure 1. A'170 Figure 3is a part sectional lside elevation of a modiied construction of pick-upmounted upon a counter balanced tone arm, said arm having associatedtherewith means for adjusting the balance thereof.

Figure 4 is an enlarged sectional elevation of a modified constructionof pick-up shown Y in Figure 3;

Figure 5 is a front view looking in the direction of arrow X in Figurel. S0 ln one method of carrying Aout the invenn tion the pick up orcollector comprises a permanent magnet l of horseshoe formation havingcoils 2 wound on pole tips la one of which projects inwardly from eachlimb of 85 the magnet. On an insulating bar 3 extendving across themagnet are a pair of terminals 4 for the'coil windings,.and the inducedcurrents from said terminals are suitably amplified and conveyed to asuitable reproducing instrument such asa loud speaker. A split metalsocket 5 is provided at the one side of the device for attachment to thetone arm of a gramophone.

Dependinglbetween the pole tips laris a Ametal reed 7, preferably ofrectangular cross section, suitably anchored to a `member 6. This member6 is rigidly connected by a screw 6a and nut 6?) to a back plate 1bwhich 100 may be screwed to the rear of the -inagnetl and shaped at itsupper edge to conform to the curvature of the said magnet.Advantageously the fixing of the reed is approximately midway in theheight of the magnet.

The reed is bored vertically at its lower or free end to receive agramophone needle 8, which latter is detachably fixed in position so asto projectdownwardly by a screw 9 inserted laterally into a threadedhole in the reed.

The needle fixing screw 9 is preferably a thumb screw and the length ofsame is such that the screw head projects out clear of the magnet coils2 and can be manipulated with ease by the fingers without touching thecoils.

The pole tips 1a upon which the magnet` coils 2 are mounted are oftubular formation and each may be adjustably fixed in position by ascrew 10 which is inserted through a plain hole in the magnet endportions 1c and into an internally threaded part of the bore of the polepiece. Each pole tip projects inwardly beyond the coil 2 and theinnermost half or part of the bore .is preferably of increased diameterso as to accommodate a loose metal piece 11 and a small piece of rubber12 or equivalent non-conductive resilient material.

This rubber element 12 projects a little way beyond the inner face ofpole piece la, and it will be appreciated that the two rubber elementslocated one on each side of the reed 7 constitute dampers functioningnormally to hold said reed centrally between the magnet poles andpreventing promiscuous lateral movement of the reed.

The aforesaid screws 10 are hollow, and within each of said screws is afurther screw 13 bearing at its inner end on the loose metal piece 11.The axial adjustment of this inner screw 13 effects an adjustment of thesaid loose piece 11 and damper 12, and also determines the degree ofpressure exerted by said damper on the reed.

The screw 13 is locked in its adjusted position by nut 14.

The dampers being located substantially near to the fulcrum of the reedprovides for a maximum amount of leverage of the associated reed andneedle and ensures a particularly sensitive operation thereof whenoperating upon a gramophone record, thus producing exceptionallyaccurate and clearly defined results in the loud speaker.

In a modified arrangement illustrated in Figures 3 to 5 the horseshoemagnet v1 is mounted upon a back plate 15 which has cast integrallytherewith a boss 16 by which the pick up is suitably connected to thetone .arm 17. Y Y

In this arrangement the pole pieces 1a instead of being connecteddirectly to the limbs of the magnet 1, are mounted upon angle bracketmembers 18 which are fixed to the rear plate 15 so that one fla-nge ofeach angle member projects outwardly and forwardly from said rear plate.The twoV limbs of the magnet bear upon the upstanding flanges of theangle members 18, said magnet being secured in position by an insulatedor nonmagnetic cross bar 3 which extends across the front of the magnetand is connected to the rear plate 15 by a screw, bolt or the like 19.The screw member 19 which is located centrally in the width of the pickup also serves as a means for connecting the reed 7, said reedadvantageously depending from a member 20 which also functions as aspacing sleeve between the bar 3 and back plate 15. On the plate 15 isalso suitably fixed an insulating block or member 21 carrying a pair ofterminals 22 to which wire extends from Vthe two coil windings 2 mountedon the pole pieces of the magnet.

Damping means for the reed are provided as hereinbefore described saiddamping means beingadjustable by screw adjustment also asbefore-described. In the modified arrangement, however, the screwadjustment for the reed damping means is passed through the upstandingflange of each angle member 18 instead of, as in the first describedembodiment, through each limb of the magnet.

By reasonof the fact that the adjustment, of the reed damping iseffected axially of the pole pieces, the size and weight of the actualreed or armature carrying the needle are reduced to a minimum, and theefliciency of the device consequently enhanced.

The tone arm 17 is preferably pivoted org" hingedto the upper end of ascrewed spindle member 23 (Figure 3) said spindle being adapted torotate within an internally threaded pillar 24, said tone arm having an,

enlarged portion 25 overhanging a pivot 26 so as to constitute a counterbalance for the pick up.

Advantageously the overhanging portion 25 of the arm is made hollow andaccommo-` dates a weight`27 carried by screw-threaded`Alv pin 28 passingthrough a threaded aperture in the end of said portion 25, thearrangement being such that by rotation of the pin 28 and weight 27thereon the position of said* weight relatively to the pivot 26 can beadjusted'and by so doing the balance of the tone arm can be adjusted tothe exact required degree. A milled knob 29 is provided at the end ofthe screwed pin 28 for the manipulation thereof, a fixing nut 30 beingadvantageously also provided for fixing the weight 27 at the adjustedposition.

Weclaim 1. A pick up for the electrical reproduction of sound fromrecords, embodying in combination a permanent horseshoe magnet havinghollow cylindrical pole pieces, said pole pieces being mounted onbracket members'positioned adjacent'to the two limbs of the magnet, acoil on each pole piece, a metal reed resiliently suspended between thecoils, the length of said reed approximating the diameter of the coils,a screw operating axially within each pole piece, cushion elements fordamping the reed located on each side of said reed and said screwsfunctioning adjustably to determine the position of said cushions.

2. A pick up for the electrical reproduction of sound from records,embodying in combination a. permanent horseshoe magnet, a plate on whichsaid magnet is mounted, said plate being adapted for connection to atone arm, bracket elements mounted on said rear plate adjacent to thetwo limbs of the magnet, hollow pole pieces on said brackets, a coil oneach pole piece, a reed resiliently suspended between said coils, reeddamping cushions, and said cushions being adjustable by screws locatedand operating axially of said pole pieces and coils.

3. A pick up Jfor the electrical reproduc tion of sound from records,embodying in combination a permanent horseshoe magnet, a rear platecarrying said magnet, said rear plate being connected to a tone arm, anangle bracket fixed to said rear plate adja cent te each pole of themagnet, an externally and internally threaded sleeve screwed through anupstanding part of such bracket, a hollow cylindrical pole piece carriedby each sleeve, a coil on each pole piece, a metal reed suspendedresiliently between said pole coils, means for detachably iixing aneedleto said reed, a damping cushion element on each side of said reed and ascrew member located axially of each coil and operating within eachsleeve adjustably to determine the position of the damping elementsrelatively to said reed.

A. The combination claimed in claim 3 wherein the pick up is carried bya hinged tone arm which is provided with counter balancing means.

5. The combination claimed in claim 3 wherein the pick up is carried bya hinged tone arm having counter balancing means which are adjustable toadjust the balance of the arm.

LAURENCE HERBERT PEARSON.

CLAUDE MARSHALL.

